1. Field of the Invention
This invention relates to specific acrylic esters and amides that can be graft copolymerized onto a cellulosic substrate to impart essentially permanent fire retardant properties to a cellulosic substrate and to cellulosic substrates copolymerized with said compounds.
2. Description of the Prior Art
Cellulosic textiles are very flammable especially when in a napped or brushed form. This hazard has been recognized for many years and a variety of methods have been employed to suppress this flammability. Some methods achieved a high level of nonflammability but were not permanent, that is, their flame retardancy was lost after one or more washings. Other methods imparted essentially permanent flame retardancy although they seriously impaired the textile qualities of the cellulosic material.
Cotton, linen and other cellulosic fibrous materials in fabric form have been impregnated with phosphoric acid, organic or inorganic ammonium salts of phosphoric acid, sulfonic acid or its organic and inorganic ammonium salts, borax, boric acid, ammonium borate and the like in order to render the cellulosic fabric flame retardant and in some cases self-extinguishing. However, such reagents usually do not combine chemically or physically to the fabric and water leaches out the beneficial fire retardant property.
Thermosetting resins, rich in phosphorus and nitrogen, have been devised which when patted on the cellulosic substrate and consequently cured with heat in the presence of a catalyst, improves the permanent (durable) nature of the non-flammable characteristic of the treated fabric. Flame retardancy achieved by this technique usually is durable to a number of home launderings but the fabric so treated suffers from a loss of hand, loss of tear strength and a reduction in abrasion resistance through a stiffening of the textile structure.
Reduced flammability may be imparted to synthetic cellulosic fiber such as rayon, during its manufacture by incorporating a fire retarding reagent in the viscose dope. Subsequent regeneration of such a treated dope yields cellulose (rayon) having the fire retarding reagent physically entrapped within its structure. Such fire retarding reagents must be inert to the high alkalinity of viscose dope, be capable of passing freely through the extremely fine orifice of the rayon spinnerette and capable also of withstanding the action of the highly acidic regeneration bath and subsequent finishing steps of the rayon process. In addition, the reagent should be insoluble in water and the usual dry cleaning solvents. To satisfy all these requirements is both costly and technically difficult.
Graft copolymerization of cellulosics (fiber or fabric) with a phosphorous or halogen containing vinyl compound has been shown to impart a degree of flame retardancy to the grafted substrate. The presence of amino (or amido) nitrogen groups enhances the fire retardant action. However, halogen containing vinyl compounds should have a relatively labile halogen atom in order to be effective but with such compounds the grafted cellulosic substrate gradually loses strength through the depolymerization of its cellulose backbone by the catalytic action of the halogenic acid being slowly liberated.